HCS320 datasheet(11/32 Pages) MICROCHIP

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DS41097C-page 11

HCS320

5.0

SPECIAL FEATURES

5.1

Code Word Completion

Code word completion is an automatic feature that

makes sure that the entire code word is transmitted,

even if the transmit button is released before the trans-

mission is complete. The HCS320 encoder powers

itself up when a button is pushed and powers itself

down after the command is finished, if the user has

already released the button. If the button is held down

beyond the time for one transmission, then multiple

transmissions will result. If another button is activated

during a transmission, the active transmission will be

aborted and the function new code will be generated

using the new button information.

5.2

Auto-Shutoff

The Auto-shutoff function automatically stops the

device from transmitting if a button inadvertently gets

pressed for a long period of time. This will prevent the

device from draining the battery if a button gets

pressed while the transmitter is in a pocket or purse.

This function can be enabled or disabled and is

selected by setting or clearing the Auto-shutoff bit

(Section 3.4.1). Setting this bit high will enable the

function (turn Auto-shutoff function on) and setting the

bit low will disable the function. Time-out period is

dependent on the shift level and is approximately 42

±10 seconds.

5.3

VLOW: Voltage LOW Indicator

The VLOW bit is transmitted with every transmission

(Figure 8-6) and will be transmitted as a one if the oper-

ating voltage has dropped below the low voltage trip

point. The trip point is selectable between two values,

based on the battery voltage being used. See

Section 3.5.4 for a description of how the low voltage

select option is set. This VLOW signal is transmitted so

the receiver can alert the user that the transmitter bat-

tery is low.

5.4

RPT: Repeat Indicator

This bit will be low for the first transmitted word. If a

button is held down for more than one transmitted code

word, this bit will be set to indicate a repeated code

word and remain set until the button is released.

5.5

LED Output Operation

During normal transmission the LED output (Figure 5-1)

indicates the shift level (Section 5.7) by flashing the

LED in a pattern corresponding to the shift level. If the

supply voltage drops below the low voltage trip point

(Section 3.5.4), the LED output will be toggled at

approximately 5 Hz during the transmission.

FIGURE 5-1:

LED FLASH FUNCTION (EACH DIVISION - 180 MS)

Note:

Depending on the internal resistance of the

VDD source, VDD may normally be above

the VLOW trip point except when the LED is

turned on. In this case, the VLOW bit will be

transmitted as a one when a transmission

occurs while the LED is on. The VLOW bit

will be transmitted as a zero when a trans-

mission occurs while the LED is off.

SHIFT

LEVEL

LED OUTPUT

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